Gain insights into Jest, a versatile testing framework. Learn about fundamental and advanced testing techniques, from unit tests to CI/CD integration, for comprehensive JavaScript application testing.

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Run Tests

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Jest is a framework for testing applications developed in JavaScript. It has a well-documented and well-maintained range of tools to run tests in parallel. It is simple and works with projects using Babel, TypeScript, Node, React, Angular, Vue, etc. It works well for both client and server testing. 

This course covers Jest in-depth and is agnostic of any specific JavaScript framework. The course begins with the fundamentals of Jest testing, deconstructing the components of a test and covering how to compose basic unit tests and snapshot tests with Jest correctly. Next, it shows the testing of asynchronous code and the code that relies on external dependencies. Lastly, this course illustrates how Jest testing can effectively integrate into the real-world software development cycle through CI/CD pipeline.

It gives you hands-on experience in setting up Jest, types of testing, testing coverage, mocking, and native tooling depth.

…. To come 

… to come 

Mastering Jest: A Complete Guide to Testing

# Navigating the failing tests

What do we do when a test fails? 

When a test fails, one of two things is happening:


1. Our code is not doing what we think it’s doing.

2. Our test is not testing what we think it’s testing.


As a general rule, fix the code, not the tests. Tests should not be written to pass. They should be written to test our assumptions of how our code works and should pass because our code meets our expectations. If tests fail, the code should be fixed to execute as expected.

However, sometimes tests need to be updated to reflect changes in the codebase. Although, it is best to write tests so that implementation details are not being tested to avoid needing to update them regularly. Usually, the first pass at writing a test isn’t quite right and requires some tweaking to get it across the finish line. In these instances, we need to debug our tests to see why they aren’t passing.

# Using the `debugger;` statement

As in other Node environments, we have the `debugger;` statement at our disposal. If you are not familiar with this, you can read more about it [here in the Node.js documentation](https://nodejs.org/api/debugger.html). We can add `debugger;` at any point in our code to pause execution and inspect the values of different objects and variables present in the relevant block of code.

This tool also functions inside our Jest testing environment, meaning we can add this same line at any point in our tests to pause the execution of a test and inspect its values. After placing the `debugger;` statements strategically inside of a failing test, we must run the command below inside the test directory:

```
node --inspect-brk node_modules/.bin/jest --runInBand
```

This command starts a Node process running Jest. We can then connect to this process with the debugger of our choice, such as Chrome's or VSCode's debugging tools.

# Debugging in Chrome

To debug using Chrome, perform the following steps:

1. Navigate to `chrome://inspect` in your Chrome browser.

2. Click the button that says “Open Dedicated DevTools for Node.”



Learn how to debug tests and code when our Jest tests start to fail.

Introduction

Setting Up Jest

Jest Matchers

Writing Unit Tests

Writing Snapshot Tests

Asynchronous Code

Mocking

Mocking External Libraries

Working with Jest Mocks

Setup & Teardown

Test Coverage & CI/CD Pipelines

Test Coverage in Jest

Conclusion

Bonus: Best Practices

Bonus: Resources for Continued Learning

Appendix

Debugging the Tests

Navigating the failing tests